The present invention relates to a recording medium such as an optical disk or the like, and particularly to a data format of a reproduction-only recording medium, and also relates to a reproducing apparatus and a reproducing method for the reproduction-only recording medium, and a disk manufacturing method.
As technology for recording and reproducing digital data, there is data recording technology using optical disks (including magneto-optical disks) such for example as CDs (Compact Disks), MDs (Mini-Disks), and DVDs (Digital Versatile Disks) as recording media. The optical disk is a generic name for recording media that allow a signal to be read by irradiating a disk formed by a metallic thin plate protected with plastic with laser light and detecting change in the reflected light.
Optical disks include for example reproduction-only types known as CD, CD-ROM, DVD-ROM and the like and user data recordable types known as MD, CD-R, CD-RW, DVD-R, DVD-RW, DVD+RW, DVD-RAM and the like. The recordable types allow data to be recorded thereon by using a magneto-optical recording method, a phase change recording method, a dye film change recording method and the like. The dye film change recording method is also referred to as a write-once recording method, which allows data recording only once and does not allow rewriting. The dye film change recording method is therefore suitable for data storing purposes and the like. On the other hand, the magneto-optical recording method and the phase change recording method allow data rewriting, and are used for various purposes including recording of various contents data such as music, video, games, application programs and the like.
In addition, high-density optical disks referred to as DVR (Data & Video Recording) or Blu-ray disks have recently been developed to increase the capacity significantly.
In a disk structure of such a high-density disk as DVR with a 0.1 mm cover layer in a direction of thickness of the disk, phase change marks are recorded and reproduced under conditions of a combination of a laser (so-called blue laser) having a wavelength of 405 nm and an objective lens having an NA of 0.85. Supposing that a track pitch is 0.32 μm and a linear density is 0.12 μ m/bit with a data block of 64 KB (kilobytes) as one recording and reproducing unit, and supposing that format efficiency is about 82%, a volume of about 23.3 GB (gigabytes) can be recorded and reproduced on a disk 12 cm in diameter.
Supposing that the linear density is 0.112 μm/bit in the same format, a volume of about 25 GB can be recorded and reproduced.
Further, a multilayer structure of a recording layer can dramatically increase the capacity. For example, by making the recording layer of two layers, the capacity can be double the above capacity, that is, 46.6 GB or 50 GB.
On a reproduction-only disk, for example a DVD-ROM of the above-mentioned various optical disks, data is recorded as pits created in advance (embossed pits or the like) basically in units of error correcting blocks.
In a conventionally known data format of the reproduction-only disk, units of error correcting blocks are recorded continuously without a break. This means that an error correcting block is a block of one recording and reproducing unit, and that no linking area (buffer area) is formed between blocks.
As with the reproduction-only disk, data is recorded and reproduced on recordable disks (recording and reproducing disks) basically in units of error correcting blocks.
However, a linking area may be formed between blocks in consideration of random access recording characteristics.
Using linking has an advantage in that when a recording and reproducing apparatus realizes block random access, the block random access can be realized by simpler and less expensive hardware than in a data format without linking.
Disk format techniques with linking are disclosed in the following literature, for example.
[First Patent Literature]                U.S.Pat. No. 5,528,569        
[Second Patent Literature]                U.S.Pat. No. 5,552,896        
Consideration will now be given to a reproduction-only disk and a recording and reproducing disk as fundamentally the same type of disk. For example, the reproduction-only disk is a DVD-ROM and the recording and reproducing disk is a DVD-RAM or the like. Alternatively, the reproduction-only disk and the recording and reproducing disk are the above-mentioned high-density disk (DVR).
Reproduction compatibility between disks of the same type is required. The compatibility is decreased when a data arrangement system (data format) differs between the reproduction-only disk without linking and the recording and reproducing disk with linking, for example.
Specifically, a reproducing apparatus supporting both disks in such a case needs to have two similar pieces of hardware or software as reproduction timing generating circuits, synchronizing circuits, firmware and the like for the reproduction-only disk and the recording and reproducing disk, and switch between the two similar pieces of hardware or software according to a disk to be reproduced. That is, burdens on configuration of the apparatus are increased to maintain the compatibility.
Accordingly, there is a proposition that the format of the above-mentioned high-density disk have linking areas also on the reproduction-only disk, for example.
However, when linking is provided for the reproduction-only disk where data is recorded by embossed pits as the above-mentioned high-density disk, for example, the following problems occur.
A rewritable disk as the high-density disk has a groove formed thereon in a spiral shape, and has phase change marks recorded and reproduced along the groove.
For a tracking servo to apply laser light along the groove, a tracking error signal formed by a push-pull signal is used.
Consideration will be given to a reproduction-only disk (hereinafter referred to as a ROM disk) having embossed pits formed with the same density and the same data format as those of the rewritable disk.
The rewritable disk has a shallow groove of about λ/10 (λ=laser wavelength) formed thereon to reduce media noise.
On the other hand, for a high level of a reproduced RF signal, it is desirable to form pits about λ/4 deep on the ROM disk.
However, from a viewpoint of the tracking servo, it is desirable to form pits about λ/8 deep for a high level of the push-pull signal.
It is therefore difficult to determine conditions for forming the ROM disk when the tracking servo using the push-pull signal is a precondition.
In addition to the method using the push-pull signal, a DPD (Differential Phase Detection) method is known as a tracking error signal detection method. A DPD signal becomes high in level by pits of a depth of λ/4, which is the same condition as for the reproduced RF signal. The DPD signal is therefore desirable for the ROM disk. Thus, using the DPD signal as a tracking error signal for the ROM disk has been considered.
However, the DPD signal does not have a sufficient signal level when pit patterns of adjacent tracks are the same.
In this case, linking areas on the ROM disk which areas are set in consideration of compatibility with the rewritable disk as described above become a problem.
Linking areas at front ends and rear ends of blocks on the rewritable disk where recording and reproduction are performed in block units are intended for PLL synchronization and protection of recorded data. The linking areas use for example a fixed preamble pattern for PLL processing or the like.
In the case of the ROM disk provided with linking areas in consideration of such a compatibility with the rewritable disk, when linking areas are aligned with each other on adjacent tracks, pit patterns of the adjacent tracks in that part are the same. Therefore, a sufficient level of a DPD signal is not obtained at such a part, which may affect the tracking servo.